The location Irs, CT has an unique ZIP Codes assigned (06176). Although this location name (Irs, CT) is set as NOT ACCEPTABLE (meaning it is an inadequate city name). So looking for the ZIP Code 06176 we have found out the following locations (for your mailing or form filling you should use an ACCEPTABLE or PRIMARY location name).
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PRIMARY: means an the primary city name. Official city name, although the city name might also have another acceptable name.
ACCEPTABLE: means an adequate city name. City names that are abbreviated will frequently be listed as unacceptable because abbreviations are not an acceptable city name format.
IMPROPER/NOT ACCEPTABLE: Means an inadequate city name has been entered or received based on information entered.
UNIQUE: Assigned to a company, government agency, or entity with sufficient mail volume, based on average daily volume of letter size mail received, availability of ZIP Code numbers in the postal area, and the US mail service cost-benefit analysis.